NEVPNProtocolIPSec Certificate Not Trusted (iOS 8)

I'm trying to setup a VPN connection from code. I'm able to do most of the configuration I need. However, when I've installed the VPN configuration, under 'Signed by' it says 'Not Signed'. I would like to sign the certificate with another certificate, but I'm not sure how I can do that.

This is the code I've got so far.

[vpnManager loadFromPreferencesWithCompletionHandler:^(NSError * __nullable error) {
     if ([vpnManager protocol] == nil) {

          NEVPNProtocolIPSec *protocol = [[NEVPNProtocolIPSec alloc] init];
          protocol.serverAddress = @"vpn.server.com";
          protocol.authenticationMethod = NEVPNIKEAuthenticationMethodCertificate;
          protocol.useExtendedAuthentication = YES;
          NSURL *pkcs12URL = [[NSBundle mainBundle] URLForResource:@"Certificates" withExtension:@"p12"];
          NSData *identityData = [[NSData alloc] initWithContentsOfURL:pkcs12URL];
          protocol.identityData = identityData;

          vpnManager.protocol = protocol;
          vpnManager.enabled = YES;
          [vpnManager saveToPreferencesWithCompletionHandler:^(NSError * __nullable error) {
               [vpnManager.connection startVPNTunnelAndReturnError:nil];
          }];
     }
}];